Non-photographic digital Laser Image Recording of the present invention employs technologies set forth in U.S. Pat. Nos. 3,314,073 and 3,474,547 by Becker. The first of these patents discloses and claims a system of high density or megacycle frequency recording of information, comprising the production of instantaneous laser recording with a diffraction limited focused laser beam impinging on a thermally vaporizable film coating, so that the coating is removed with thermo-optical energy concentrated within its smallest possible diffraction limited diameter (d), defined as: EQU d = 1.22 .lambda. f/D
where 1.22 is a first order Bessel function, (.lambda.) is the recording laser wavelength, and f/D is the f-number of the laser focusing optics, defined as the ratio of focal length (f) and the effective aperture (D) of the system. The second patent discloses and claims a laser recording medium formed of a substrate having a high optical transmissivity and a metal coating integrally formed on said substrate, a laser generating a laser beam of a predetermined wavelength, and optical means for focusing the laser beam on the recording medium.
Prior art real time recording systems and methods were practically unavailable for recording visual images, that is, images decipherable by the human eye. However, the real time recording of binary mass memories is well known. The above referenced U.S. patents relate to the real time recording of optical mass memories defined by diffraction limited holes or spots in suitable recording media. Real time magnetic recordation of binary data on magnetic tapes, discs, and cards is equally well known and widely practiced. Both systems, however, generate records which cannot be read by the human eye, in other words, the stored data is not in visual form.
Visual recordation, other than contact printing, was primarily limited to photographic recordation. Photographic recordation, of course, is not real time recordation but requires developing times and is, therefore, relatively slow. Moverover, photographic recordation has a relatively low resolution and is frequently ill adapted for many of the high resolution, high speed requirements of present day technology.
In the more recent past, the assignee of the present application developed a printing system based on a non-photographic data recording process which also utilizes the above described metal thin film in conjunction with a laser to create limited holes in the thin film. The resulting two-dimensional ensemble of such holes in the thin film represents a directly viewable replica of the original image.
Such a laser printer comprises a reading section that cooperates with part of a double drum rotating system. One of the drums holds the picture to be printed. The picture is scanned with a reading laser beam by employing a reading objective mounted to a linear transport that is phase locked to the drum rotating mechanism.
The other drum mounts the metal thin film on which the original picture is reproduced, normally at a reduced size, with the printing laser. The beam from the printing laser is externally modulated and projecting through an objective capable of diffraction limited focusing of the beam. The focused beam impinges on the metal film and burns holes therein of minimal size. The printing objective is mounted on a linear translator, the mechanical motion of which is controlled by a phase locked servo mechanism. As the drum rotates at speeds up to 3,000 rpm the printing objective is linearly translated perpendicular to the direction of drum rotation at the required rate to obtain the desired picture resolution.
Thus, this recently developed laser printer enables the high resolution real time printing of data in visual form. However, its printing speed is limited by the rotating speed of the drum which for practical purposes, cannot be much higher than 3,000 rpm. Moreover, the registration of the film and the objective is a mechanical registration which is subject to inherent limitations in its accuracy and, where the highest precision is required, is further very expensive to produce, operate and maintain in satisfactory working order. Thus, the prior art is devoid of an economically producable and operable high speed real time visual image reading and recording system.